"Epic's tool that lets you make realistic digital humans is now in early access". "Evidence for variable selective pressures at MC1R".
Black hair freckles skin#
"Association of melanocortin 1 receptor gene (MC1R) polymorphisms with skin reflectance and freckles in Japanese".
Robbins and Cotran Pathologic Basis of Disease (7th ed.). Freckled individuals tend to tan less and have very light skin, which would have helped the individuals that expressed these genes absorb vitamin D. The adaptation of lighter skin is needed so that individuals in higher latitudes can still absorb enough UV for the production of vitamin D. The need was less as humans moved into higher latitudes where incoming sunlight has lower UV light content. The high melanin content is protective in areas of high UV light exposure. The original allele of MC1R is coded for dark skin with a high melanin content in the cells. The wide variation of the MC1R gene exists in people of European descent because of the lack of strong environmental pressures on the gene. Arg160Trp is estimated to have arisen around 80,000 years ago while Arg151Cys and Asp294His have been estimated to arise around 30,000 years ago. The variant Val92Met arose somewhere between 250,000 and 100,000 years ago, long enough for this gene to be carried by humans into central Asia.
The variants of the MC1R gene that are linked with freckles started to emerge in the human genotype when humans started to leave Africa. The R162Q allele has a disputed involvement in freckling. These individuals have the variant Val92Met which is also found in white people, although it has minimal effects on their pigmentation. Freckling can also be found in areas, such as Japan, where red hair is not seen. The variants that cause red hair are the same that cause freckling. Most red-haired individuals have two variants of the MC1R gene and almost all have one. The MC1R gene is also associated with red hair more strongly than with freckles. Of the variants of the MC1R gene Arg151Cys, Arg160Trp, and Asp294His are the most common in the freckled subjects. Even so, individuals with a high number of freckling sites have one or more of variants of the MC1R gene. Also, individuals with no copies of the MC1R do sometimes display freckles. The presence of freckles is related to rare alleles of the MC1R gene, though it does not differentiate whether an individual will have freckles if they have one or even two copies of this gene. It is suggested that people whose skin tends to freckle should avoid overexposure to sun and use sunscreen. Upon exposure to the sun, freckles will reappear if they have been altered with creams or lasers and not protected from the sun, but do fade with age in some cases.įreckles are not a skin disorder, but people with freckles generally have a lower concentration of photo-protective melanin, and are therefore more susceptible to the harmful effects of UV radiation. Freckles are rare on infants, and more commonly found on children before puberty. Heavily distributed concentrations of melanin may cause freckles to multiply and cover an entire area of skin, such as the face. This means that one who has never developed freckles may develop them suddenly following extended exposure to sunlight.įreckles are predominantly found on the face, although they may appear on any skin exposed to the sun, such as arms or shoulders. The exposure to UV-B radiation activates melanocytes to increase melanin production, which can cause freckles to become darker and more visible. The formation of freckles is caused by exposure to sunlight.
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